1. Field of the Invention
The present invention relates to an exhaust pump that is used, as gas evacuation means or the like, in a process chamber of a semiconductor manufacturing apparatus, a flat panel display manufacturing apparatus or a solar panel manufacturing apparatus, and in other sealed chambers; more particularly, the present invention relates to an exhaust pump exhibiting enhanced durability, processability of connecting opening portions during the production stage of the pump, and also improved evacuation performance.
2. Description of the Related Art
One known method for enhancing the evacuation performance of an exhaust pump of a type where gas is evacuated by using a thread groove, but without modifying the overall size of the pump, is, for instance, the method disclosed in Japanese Utility Model Application Laid-open No. H5-38389.
In this method, as illustrated in FIG. 1 of Japanese Utility Model Application Laid-open No. H5-38389, thread grooves (30, 31) are provided at the outer periphery and the inner periphery of a cylindrical rotating member (4a). As a result, a helical outer thread groove exhaust passage becomes formed between the cylindrical rotating member (4a) and an outer cylindrical fixed member (33) that surrounds the outer periphery of the cylindrical rotating member (4a), and a helical inner thread groove exhaust passage becomes formed between the cylindrical rotating member (4a) and an inner cylindrical fixed member (7) that is surrounded by the inner periphery of the cylindrical rotating member (4a), such that gas molecules are evacuated in parallel along these inner and outer thread groove exhaust passages.
In order to lead the gas molecules to the inner thread groove exhaust passage in the exhaust pump that utilizes the above method, however, a configuration is resorted to wherein connecting opening portions (4b) are opened at a connection ring section (unmarked with a reference numeral) of the cylindrical rotating member (4a). As a result, stress concentration arises at the edges of the connecting opening portions (4b) upon deformation of the cylindrical rotating member (4a) due to, for instance, centrifugal force and/or thermal expansion of the cylindrical rotating member (4a) when the cylindrical rotating member (4a) rotates about the axis thereof. Durability is thus problematic, in that the rotor (4) becomes likely to break from the vicinity of the connection ring section (unmarked with a reference numeral) where the connecting opening portions (4b) are formed.
In an exhaust pump that utilizes the above-mentioned method, rotor blades (5) exist above the connecting opening portions (4b), as can be seen in FIG. 1 and FIG. 2 of Japanese Utility Model Application Laid-open No. H5-38389. As a result, the connecting opening portions (4b) must be opened through insertion of a tool from a lower opening of the cylindrical rotating member (4a) into the inner periphery of the cylindrical rotating member (4a) (refer to the processing using the tool T4 of FIG. 2A) of the present application). Therefore, a long tool is required, which translates into problems of processability of the connecting opening portions (4b), for instance tool runout during opening of the connecting opening portions (4b) if the rigidity of the support system of the tool is poor.
The exhaust pump that utilizes the above method has enhanced evacuation performance. However, recent years have witnessed an increase in the size of the sealed chambers, and in the amount of gases, such as reactive gases and the like, that are used in these chambers, as dictated by the increase in size of the semiconductors, flat panels, solar panels and the like that are produced in such sealed chambers. Accordingly, yet better evacuation performance is required from exhaust pumps as means for evacuating such gases.
The reference numerals in brackets in the explanation above denote reference numerals used in Japanese Utility Model Application Laid-open No. H5-38389.